Fan system



H. F. HAGEN FAN SYSTEM- Elecf'ric Source Filed April 6, 1939 Cansfa. n1

v me So u rce m? W 3 n. IF 0 m M H PLANT LOADS msmwmuk Patented May 28, 1940 PATENT OFFICE FAN SYSTEM Harold F. Hagen, Wcllesley, Mass, assignor to B. F. Sturtcvant Company, Hyde Park, Boston,

Mass.

Application April 6,1939, Serial No. 266,324

9 Claims.

This invention relates to fan systems and relates more particularly to a fan system providing forced and induced draft in balanced relationship.

This application is a continuation-impart of my copending application Serial No. 95,675, filed August 12, 1936 and which issued as Letters Patent No. 2,160,968 on June 6, 1939.

Modern steam power plants ordinarily use forced draft fans for supplying air under pressure to the burners for combustion, and use separate induced draft fans usually spaced a substantial distance from the forced draft fans for drawing the furnace gases through the heat exchangers and for discharging the exhaust gases from the stack. The forced draft fan usually takes care of the air resistance of a steam plant as far as the top of the fuel bed. The induced no draft fan usually takes care of the resistance from the fire box through the boiler and economizer.

In a typical steam plant for a given plant load,

a pressure corresponding to 4 inches of water may be provided by the forced draft fan and a static suction corresponding to 2 inches of water may be provided by the induced draft fan. The pressure drop or pressure differential through the plant in such a case is 6 inches of water of which 4 inches is provided by the forced draft and of which 2 inches is provided by the induced draft fan.

For different plant loads, different quantities of fuel are burned and different volumes of air are required for efficient combustion. For supn plying different air volumes into the combustion chamber, different pressures are required from the forced draft fan, and different static suctions are required from the induced draft fan for draw.- ingthe air with the products of combustion from the chamber. The'characteristics of a steam plant are such, however, that the proportions of the pressure differential required from the two fans for different loads and air volumes, are not constant. As the plant load decreases and the volume of air required for efficient combustion is conformably decreased, the proportion of the pressure differential required from the forced draft fan increases and the proportion required from the induced draft fan decreases. This is to due to adjustment of fuel burning and associated apparatus at reduced loads which result in greater forced draft requirements.

In the .past it has been the practice to drive the forced and induced draft fans by separate 3 motors with separate controls for varying the ill speeds of the motors so that the adjustment of one had little or no effect upon the other.

In my said application there is disclosed a forced draft fan and an induced draft fan having their wheels mounted on a single shaft and driven by a single motor. Among the advantages of such an arrangement are: less space is required; smaller and cheaper foundations may be used; two bearings, two pedestals may be eliminated; the flue arrangement may be simplified; and the first cost, operating cost and cost of maintenance are less. To provide the desired air pressure for combustion, the speed of the single motor driving the two fans is varied conformably with load changes. The speed of the induced draft fan and its capacity is of course reduced as the speed of the driving motor is reduced but due to the characteristics of the steam plant being such that it is necessary at reduced loads, to reduce the pressure differential required from the induced draft fan a larger percentage than that required from the forced draft fan, spin inducing vanes were provided in the inlet of the induced draft fan to further decrease the pressure differ ential provided by the induced draft fan to prevent its producing too great a suction.

According to this invention a single, constant speed motor drives both the forced draft and the induced draft fans. Spin inducing vanes are provided in the inlet of the forced draft fan and these are adjusted conformably with load changes to vary the air pressure and the corresponding air volume supplied to the combustion chamber. Butterfly type dampers in the connection to the inlet box of the induced draft fan are also adjusted conformably with load changes to vary the suction of the induced draft fan. Spin inducing vanes in the inlet of the induced draft fan are adjusted conformably with suction changes in the combustion chamber for preventing the induced draft fan from producing too great suctions at reduced loads.

Constant speed motors which may be of the squirrel cage induction motor type are less expensive and more eflicient especially at reduced loads, than variable speed motors; spin inducing vanes in the inlet of the forced draft fan permit highly efficient pressure and volume control, and these features of economy added to those previously described as resulting from combining the forced and induced draft fans in a single unit, result in a very efficient and economical fan system for steam plants.

An object of theinvention is efliciently to profill vide the forced and induced draft requirements of a steam plant.

Another object of the invention is economically to provide the forced and induced draft requirements of a steam plant.

Another object of the invention is to drive in a steam plant a forced draft fan and an induced draft fan by a single motor, to adjust the air volume by adjustment of spin inducing vanes in the inlet of the forced draft fan, and to compensate for furnace pressiu'e changes by adjustment of spin inducing vanes in the inlet of the induced draft fan.

Other objects of the invention will be apparent from the following description taken together with the drawing.

The invention will now be described with reference to the drawing, of which:

Fig. 1 is a diagrammatic view of a fan system with controls embodying this invention, and

Fig. 2 is a chart illustrating the requirements of the steam plant of Fig. 1 from the forced draft fan and from the induced draft fan at different plant loads.

Referring first to the chart of Fig. 2, the abscissa entitled Plant loads represents the loads under which it is expected the steam plant of Fig. 1 will be operated. The ordinate entitled Pressure differentials represents the pressure differentials required by the plant from the two fans at different plant loads. The curve entitled Total from both fans represents the pressure differentials required by the plant from both fans at different plant loads. The curve entitled "Forced draft fan represents the pressure differentials required by the plant from the forced draft fan at different plant loads. The curve entitled Induced draft fan represents the pressure differentials required by the plant from the induced draft fan at different plant loads. For the purpose of illustration, at the maximum plant load, the forced draft fan is shown to provide 4 inches and the induced draft fan to provide 2 inches, of a total of 6 inches of pressure differential required for providing the volume of air required to efficiently burn the fuel supplied to the plant.

Under lighter loads, less fuel is burned, reduced volumes of air and lower pressure differentials are required. But, for reduced loads the forced and induced draft fans do not provide the same proportions of the pressme differentials through the plant that they do at maximum plant load. The chart of Fig. 2 shows that for loads below the maximum, the forced draft fan is required to provide greater proportions and the induced draft fan is required to provide less proportions of the pressure differentials. If the total volume is adjusted in accordance with forced draft requirements as is preferred, without independent adjustment of the induced draft fan, the induced draft fan would be operated to produce too great a suction in the combustion chamber. This invention provides for adjusting the air volume supplied to the plant, in accordance with the forced draft requirements at different loads by adjustment of vanes in the outlet of the forced draft fan, for adjusting the suction of the induced draft fan conformably with load changes, and for additionally adjusting the suction of the induced draft fan, by adjusting vanes in the inlet of the induced draft fan. In other words, this invention provides for causing the performances of the two fans to follow the two lower curves of Fig. 2 to overcome their tendency to follow curves which would be substantially equidistant along their lengths.

In the embodiment illustrated, the changes in plant load cause the forced draft fan to provide the pressure differentials along the curve entitled Forced draft fan for providing variable volumes of air for forced draft, and simultaneously attempts to cause the induced draft fan to provide the pressure differentials along the curve entitled Induced draft fan. A suction control preferably mounted in the combustion chamber then adjusts the induced draft fan if necessary, to cause it to exactly provide the pressure differentials desired from it.

The forced draft fan 5, with inlet vanes 4, is preferably of the general type disclosed by my Patent No. 1,989,413, with a single inlet. The induced draft fan 6 with inlet vanes 65 is preferably similar to the one disclosed by my Patent No. 1,846,863 with the exception that in the present case, a fan with a single inlet is illustrated. The two fans 5 and 6 have their wheels mounted for rotation upon the same shaft 1, which is rotated by the constant speed electric motor 8.

The adjustable spin inducing vanes 4 are mounted in the inlet of the forced draft fan 5 and their function, arrangement and adjustment are disclosed in my Patent No. 1,989,413. The details of the adjustment of the vanes is not, therefore, shown here, it being believed to be sufficient to state that the rod 66 of Fig. 1 hereof corresponds to the rods 4 of Fig. 2 of said patent and as the rod 66 is raised and lowered by the solenoid 6?, as will be explained later, the vanes 4 are adjusted towards their opened and closed positions, respectively.

Mounted within the inlet chamber 9 of the induced draft fan 6 are the adjustable vanes 65, the function, arrangement and adjustment of which, are identical with the disclosure of my said Patent No. 1,846,863, and so will not be described in detail here. It is believed sufficient to state that the cranks and links, etc., indicated generally by it are adjusted by the rotation of the gear H, corresponding to the gear indicated by 48 in my said patent. The gear ll is in turn rotated by the gear l2 mounted on the same shaft as the gear 13 which is rotated by the gear 15, mounted on the shaft of the motor l6,

through the intermediary of the chain or belt I l. Rotation of the armature of the motor [6 in one direction adjusts the vanes 65 towards their full open position and rotation of the armature in the other direction adjusts the vanes towards their closed position. The operation and direction of rotation of the motor l6 are controlled by the relays ll and IS which in turn are controlled by the furnace pressure controller indicated generally by 19, as will be explained in more detail in the following.

The header 26 of the steam plant indicated generally by El is connected by the pipe 22 to the pressure chamber 23 which acts upon increases in pressure to move the lever arm 24 against the force of the weights 25 26, upwardly to cause its contact 27 to adjust the value of the resistance 28 in the circuit including the wire 29, the three solenoid coils 30 of the furnace pressure controller IS, the wire 3!, the armature 32 of the galvanometer indicated generally by 36, the wire 33, the constant voltage source 34 and the wire 35.

A diaphragm of the chamber 23 raises and lowers the lever 24 in accordance with changes in the steam pressure in the header 20, which and spring are a measure of the boiler load. As the load decreases and the pressure increases, more of the resistance 28 is placed in the above described circuit causing a decreased current to flow through the solenoids 30 and the coil 32 of the galvanometer 36.

This causes the coil 32 to adjust the contact arm 31 and increase the value of the resistor 38 included in the circuit including the arm 31, the resistor .38, the wires 39, the solenoid 61 and the electric source 40. This causes the solenoid 61 to lower the rod 65 to adjust the vanes 4 towards closed position to reduce the air volume supplied by the fan 5.

The solenoid 68 is connected in shunt with the solenoid 61 and as the latter adjusts the vanes of the forced draft fan towards closed position, the solenoid 68 through its armature 69 and link 10 adjust the butterfly type damper 1| towards closed position to reduce the suction of the induced draft fan 6. The characteristics of this equipment for adjusting the performances of the forced and induced draft fans are selected to cause the fans to follow the curves of Fig. 2. In the event the induced draft fan will not exactly follow its curve, the additional equipment now to be described is provided.

The furnace pressure controller I9 may be similar to that disclosed in U. S. Patent No. 1,870,984 to Edward S. Bristol, and illustrated in detail by Figs. 2 and 3 thereof. As shown by Fig. 1 hereof, the pivoted lever 4| has mounted upon an upright extension, the movable magnetic coil 30a. The lever 4| has mounted at one end on its underside the bell 42, the interior of which communicates through the pipe 43 with the combustion chamber of the boiler. Air, at atmospheric pressure is introduced through the pipe 44 to the exterior of the bell. As explained in said patent to Bristol, the position of the movable coil 300. will depend upon the strength of current flow through the coils and upon the difference in pressure between the upper and lower sides of the lever 4|. The upper side of the lever is exposed through the pipe 44 to atmos pheric pressure which may be assumed to be constant so that the conflicting forces acting to unbalance the lever 4| are the suctions in the bell 42 caused by the furnace draft, and the current flow through the coils caused by changes in plant load. The lever 4| carries the contact 45, which when the forces exerted by the bell 42 and the solenoids 30 and 300. are balanced, is midway between the contacts 46 and 41. When the forces are unbalanced, the contacts carried by the arms 45 will contact with one or the other of the contacts 46 and 41, causing one or the other of the relays l1 and IE to become energized to cause the motor Hi to adjust the inlet vanes of the induced draft fan 6 to restore the balanced condition between furnace draft and load by ad justing the suction in the combustion chamber. Where a constant furnace draft is desired, the contact arm 18 may be moved from the contact I 19 on the wire 29 to the contact 10 on the wire ll.

This removes the coils 30 and 32a from the circuit and cuts in the equivalent resistor 12. The bell l9 then responds only to furnace pressure.

The current flow through the resistor 28 and coil 32 Varies with the boiler load and it is desired to adjust the air volume through the furnace accordingly. Too great an increase in the furnace vacuum caused by too great a suction being applied by the induced draft fan 6, causes theforce exerted by the bell 42 to overcome the opposing force caused by the current flow through the solenoids 30 and 30a, and the lever 4| tilts to the right (facing the drawing) causing the circuit including the contact 46, the contact on the arm 45, the wire 48, the solenoid of the relay |8, the electric source 49 and the wire 50 to be completed causing the solenoid of the relay Hi to close circuits to connect the armature and field of the motor l6 together and to the current source 49 to cause the motor to rotate in a direction to adjust the vanes in the inlet chamber 9 of the induced draft fan 6 towards closed position. The motor will rotate until the vanes are adjusted to cause the proper decreased vacuum in the combustion chamber.

Too small a suction in the combustion cham ber results in the force caused by the current flow through the solenoids 30 being greater than the force exerted by the bell 42 so that the lever 4| tilts to the left causing the circuit including the contact 41, the wire 5|, the relay I1, the electric source 49,'the wire 50 and the contact 45 to be closed causing the relay H to become energized and the relay l8 to become deenergized. The relay 11 then closes contacts connecting the armature and field of the motor IE to the source l4 but in reverse relation to each other so that the motor H3 rotates in reverse direction to adjust the vanes in the inlet chamber 9 of the induced draft fan 6 towards their open position. The motor will again continue to adjust the vanes until the proper vacuum is established in the combustion chamber.

If desired, the solenoid 68, its armature 69, the link 10, and the butterfly type damper 1| may be omitted in which case the equipment described as actuated by suction changes in the combustion chamber would be designed to adjust the induced draft fan to cause it to follow its curve of Fig. 2.

While the vanes 65 in the inlet to the induced draft fan 6 have been described as adjusted conformably with suction changes in the combustion chamber, and the damper 1| has been described as adjusted conformably with load changes, the vanes 65 could be adjusted conformably with plant load changes, and the damper 1| could be adjusted conformably with suction changes in the combustion chamber.

While one embodiment of the invention has been described for the purpose of illustration, it should be understood that the invention is not limited to the exact apparatus and arrangement of apparatus described, since many departures may suggest themselves to those skilled in the art without departure from the essence of the invention.

I claim:

1. A fan system for a steam plant adapted to be operated under different loads and including a boiler having a combustion chamber adapted to receive air volumes varying conformably with said loads, comprising in combination, a forced draft fan for supplying air into said chamber, an induced draft fan for drawing the air with the products of combustion through said plant, the wheels of said fans being mounted on a common shaft, said fans cooperating to overcome the resistance of said plant for moving variable volumes of air therethrough, the suction supplied to said plant from said induced draft fan decreasing more in proportion than the'pressures applied by said forced draft fan for decreasing plant loads, means including spin inducing vanes in the inlet of said forced draft fan for varying the pressure provided thereby for varying the volume of air supplied into said chamber, means responsive to a change in the plant load for actuating said last mentioned means, volume control means in the inlet to said induced draft fan, and means including means responding conformably to changes in suction in said chamber for adjusting said volume control means to provide the suction required of said induced draft fan by said plant by said change in load.

2. A fan system for a steam plant adapted to be operated under different loads and including a boiler having a combustion chamber adapted to receive air volumes varying ccnformably with said loads, comprising in combination, a forced draft fan for supplying air into said chamber, an induced draft fan for drawing the air with the products of combustion through said plant, the wheels of said fans being mounted on a common shaft, said fans cooperating to overcome the resistance of said plant for moving variable volumes of air therethrough, the suctions supplied to said plant from said induced draft fan decreasing more in proportion than the pressures applied by said forced draft fan for decreasing plant loads, means including spin inducing vanes in the inlet of said forced draft fan for varying the pressure provided thereby for varying the volume of air supplied into said chamber, means responsive to a change in the plant load for actuating said last mentioned means, spin inducing vanes in the inlet to said induced draft fan, and means including means responding conformably to changes in suction in said chamber for adjusting said last mentioned vanes to provide the suction required of said induced draft fan by said plant by said change in load.

3. A fan system for a steam plant adapted to be operated under different loads and including a boiler having a combustion chamber adapted. to receive air volumes varying conformably with said loads, comprising in combination, a forced draft fan for supplying air into said chamber, an induced draft fan for drawing the air with the products of combustion through said plant, the

Wheels of said fans being mounted on a common shaft, said fans cooperating to overcome the re-- sistance of said plant for moving variable volumes of air therethrough, the suctions supplied to said plant from said induced draft fan decreasing more in proportion than the pressures applied by said forced draft fan for decreasing plant loads, means including spin inducing vanes in the inlet of said forced draft fan for varying the pressure provided thereby for varying the volume of air supplied into said chamber, means responsive to a change in the plant load for actuating said last mentioned means, volume control means in the inlet to said induced draft fan, and means including said means responsive to a change in. the plant load and including means responding conformably to changes in suction in said chamber for adjusting said volume control means to provide the suction required of said induced draft fan by said plant by said change in load.

A fan system for a steam plant adapted to be operated under different loads and including a boiler having a combustion chamber adapted to receive air volumes varying conformably with said loads, comprising in combination, a forced draft fan for supplying air into said chamber, an induced draft fan for drawing the air with the products of combustion through said plant, the wheels of said fans being mounted on a common shaft, said fans cooperating to provide variable load for actuating said last mentioned means, ad- I ditional volume control means in the inlet to said induced draft fan, and means including means responding conformably to changes in pressure in said chamber for adjusting said last mentioned volume control.

5. A fan system for a steam plant adapted to be operated under different loads and including a boiler having a combustion chamber adapted to receive air volumes varying conformably with said loads, comprising in combination, a forced draft fan for supplying air into said chamber, an induced draft fan for drawing the air with the products of combustion through said plant, the wheels of said fans being mounted on a com.-

mon shaft, said fans cooperating to provide variable pressure differentials for moving variable volumes of air through said plant, the proportions of the pressure differentials supplied to said plant from said induced draft fan decreasing more than the proportion applied by said forced draft fan for reduced plant loads, means including volume control means in the inlets to said fans for varying the pressure differential provided by said fans, means responsive to a change in the plant load for actuating said last mentioned means, spin inducing vanes in the inlet to said induced draft fan, and means including means responding conformably to changes in pressure in said chamber for adjusting said vanes.

6. A fan system for a steam plant adapted to be operated under different loads and including a boiler having a combustion chamber adapted to receive air volumes varying conformably with said loads, comprising in combination, a forced draft fan for supplying air into said chamber,

an induced draft fan for drawing the air with the products of combustion through said plant, the Wheels of said fans being mounted on a common shaft, said fans cooperating to overcome the resistance of said plant for moving variable volumes of air therethrough, the suctions supplied to said plant from said induced draft fan decreasing rnore in proportion than the pressures applied by said forced draft fan for decreasing plant loads, means including volume control means in the inlet of said forced draft fan for varying the pressure provided thereby for varying the volume of air supplied into said chamber, means responsive to a change in the plant load for actuating said last mentioned means, spin inducing vanes in the inlet to said induced draft fan, and means including means responding conformably to changes in suction in said chamber for adjusting said vanes.

7. A fan system for a steam plant adapted to be operated under different loads and including a boiler having a combustion chamber adapted to receive air volumes varying conformably with said loads, comprising in combination, a forced draft fan for supplying air into said chamber, an induced draft fan for drawing the air with the products of combustion through said plant, the wheels of said fans being mounted on a common shaft, said fans cooperating to overcome the resistance of said plant for moving variable volumes 76 of air therethrough, the suctions supplied to said plant from said induced draft fan decreasing more in proportion than the pressures applied by said forced draft fan for decreasing plant loads, means including volume control means in the inlet of said forced draft fan for varying the pressure provided thereby for varying the volume of air supplied into said chamber, means responsive to a change in the plant load for actuating said last mentioned means, volume control means in the inlet to said induced draft fan, and means including said means responsive to a change in the plant load and including means responding conformably to changes in the suction in said chamber for adjusting said last mentioned volume control means toprovide the suction required of said induced draft fan by said change in load.

8. A fan systemfor a steam plant adapted to be operated under different loads and including a boiler having a combustion chamber adapted to receive air volumes varying conformably with said loads, comprising in combination, a forced draft fan for supplying air into said chamber, an induced draft fan for drawing the air with the products of combustion through said plant, the wheels of said fans being mounted on a common shaft, said fans cooperating to overcome the resistance of said plant for moving variable volumes of air therethrough, the suctions supplied to said plant from said induced draft fan decreasing more in proportion than the pressures applied by said forced draft fan for decreasing plant loads, means including spin inducing vanes in the inlet of said forced draft fan for varying the pressure provided thereby for varying the volume of air supplied into said chamber, volume control means change in load.

in the inlet to said induced draft fan, means responsive to a change in the plant load for actuating said two last mentioned means, spin inducing vanes in the inlet to said induced draft fan, and means including means responding conformably to changes in suction in said chamber for adjusting said last mentioned vanes.

9. Afan system for a steam plant adapted to be operated under different loads and including a boiler having a combustion chamber adapted to receive air volumes varying conformably with said loads, comprising in combination, a forced draft fan for supplying air intosaid chamber, an induced draft fan for drawing the air with the products of combustion through said plant, the wheels of said fans being mounted on a common shaft, said fans cooperating to overcome the resistance of said plant for moving variable vol umes of air therethrough, the suctions supplied to said plant from said induced draft fan decreasing more in proportion than the pressures applied by said forced draft fan for decreasing plant loads, means including spin inducing vanes in the inlet of said forced draft fan for varying the pressure provided thereby for varying the volume of air supplied into said chamber, means responsive to a change in the plant load for actuating said last mentioned means, volume control means in the inlet to said induced draft fan, and

means including said means responsive to a change in the plant load for adjusting said volume control means to provide the suction required of said induced draft fan by said plant by said HAROLD F. HAGEN. 

